Ultrasonic device for providing reversible tissue damage to heart muscle

ABSTRACT

An ultrasonic medical or surgical device creates holes in heart tissue utilizing an ultrasonic needle or probe. The ultrasonic needle is inserted into heart tissue and activated to cause cavitation of fluid surrounding the needle. The cavitation heats the surrounding tissue and causes reversible tissue damage. The ultrasonic device consists of a transducer, a needle, and a regulator. The device can be a hand held device for external application or may be a catheter device for performing a minimally invasive procedure. A temperature sensor may be positioned on the needle for sensing a temperature of the heart tissue in which the needle has been inserted.

This application is a divisional of application Ser. No. 09/164,420,filed on Sep. 30. 1998, now U.S. Pat. No. 6,283,935.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a medical/surgical device and method fortreating the heart, and more particularly, the invention relates to anultrasonic device and method for creating holes in heart tissue.

2. Brief Description of the Related Art

Currently there are a number of companies using lasers to create holesin heart tissue, for example, Cardiogenesis Corporation of Sunnyvale,Calif.; PLC Systems, Inc. of Franklin, Mass.; and Eclipse SurgicalTechnologies, Inc. of Palo Alto, Calif. Each of these companies areutilizing lasers as an energy source to vaporize heart tissue to createa plurality of holes in the heart for treating angina and heartischemia.

Angina is sever cardiac pain most often due to ischemia of themyocardium. Ischemia is localized tissue anemia due to a partial ortemporary obstruction of inflow of arterial blood. Ischemic tissue inthe heart is usually found in the left ventricle due to a partial ortemporary obstruction or constriction of the coronary arteries. Theprocedure of forming holes in the myocardial tissue of the heart isreferred to as transmyocardial revascularization (“TMR”). The purpose ofTMR is to improve blood flow to under perfused myocardium. The lasercreated TMR holes are generally formed in the left ventricle. The holesare typically 1 mm in diameter and are placed on a 1 cm by 1 cm grid.Depending on the extent of the angina and ischemia, the laser is used tomake somewhere between 10 and 50 holes. Once the holes are created, theholes are sealed off at an exterior of the heart using pressure on theepicardial surface to prevent bleeding into the pericardium.

Studies of TMR procedures on humans have had encouraging results. Forexample, studies have found a two class reduction in angina in somepatients following TMR surgery. This two class reduction of anginagreatly increases the quality of life for patients suffering fromclasses III and IV angina. Patients having classes III and IV angina maynot be able to carry on daily activities such as walking without severpain and may be frequently hospitalized due to heart pain. Following TMRsurgery some class III and IV angina patients experience minimal or noangina for up to two years following surgery. Although these studiesshow that the TMR procedure improved the patients condition and qualityof life, it is not yet clear how the formation of holes in themyocardium provides this marked improvement in patient condition.

Three hypophysis for the improvement which has been observed are that 1)blood flow through the TMR channels directly perfuses the myocardium, 2)damage to heart tissue from ablation and heat of the laser causesrelease of growth factors that result in angiogenesis, and 3)destruction of nerve pathways mask angina and prevents pain. Because thepositive results of TMR surgery last up to two years, and the channelshave closed by this time, it is believed that direct tissue perfusion isnot the sole reason for the observed improvement.

Currently TMR is being performed utilizing a laser source of energywhich forms a hole all the way through the heart tissue. Once the holesare formed by the laser, the surgeon, must cover the hole by placing afinger on the epicardial surface until the hole clots shut or thesurgeon may use a suture to close the hole. Another disadvantage of theuse of a laser is the cost. The laser energy source for use in thisprocedure costs between about $200,000 to $700,000. This creates a highcost of performing the TMR procedure. Additionally, the laser TMRprocedure vaporizes viable heart tissue.

Accordingly, it would be desirable to provide a cost effective supply ofenergy to create holes in heart tissue. It is also preferable that theenergy delivery system does not vaporize viable heart tissue, and doesnot form holes all the way through the heart tissue.

SUMMARY OF THE INVENTION

The present invention relates to a device that creates holes in hearttissue utilizing ultrasonic energy. The device consists of an ultrasonicgenerator, a regulator, and an ultrasonic needle for deliveringultrasonic energy to the heart tissue. The ultrasonic device issignificantly less expensive than the laser device. In addition, theultrasonic device does not vaporize heart tissue but instead creates azone of reversible tissue damage caused by the heating of the tissue.Thus, the present invention provides a significant advance over thecurrent laser TMR therapy.

In accordance with one aspect of the present invention, an ultrasonicdevice for treating ischemia and angina includes a needle, an ultrasonictransducer for delivering ultrasonic energy to the needle, and atemperature sensor positioned on the needle for sensing the temperatureof heart tissue in which the needle has been inserted.

In accordance with an additional aspect of the present invention, amethod of performing transmyocardial revascularization includesinserting a needle into heart tissue, and applying ultrasonic energy tothe needle for a period of time sufficient to create a zone ofreversible tissue damage surrounding the needle.

In accordance with a further aspect of the invention, a method oftreating ischemia and angina by causing reversible damage to myocardialtissue includes inserting a needle into the myocardial tissue, applyingultrasonic energy to the needle, and heating the myocardial tissue tobetween about 40° C. and about 60° C. to create a zone of reversibletissue damage around the needle.

The ultrasonic energy may be applied by inserting the needle from anexterior of the heart or may be applied minimally invasively with aneedle at the end of a catheter.

The present invention provides advantages of a TMR device which does notvaporize viable heart tissue or create holes al the way through theheart tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe preferred embodiments illustrated in the accompanying drawings, inwhich like elements bear like reference numerals, and wherein:

FIG. 1 is a cross sectional view of a left ventricle of a heart with anultrasonic device for creating holes in the heart tissue;

FIG. 2 is a side view of an ultrasonic device for creating holes inheart tissue;

FIG. 3 is a cross sectional view of a left ventricle of a heart with aminimally invasive ultrasonic device for creating holes in the hearttissue;

FIG. 4 is a side view of a needle for use in the present invention; and

FIG. 5 is a side view of an alternate needle for use in the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a device and method for transmyocardialrevascularization (“TMR”) utilizing an ultrasonic device 10 for heatingheart tissue. FIG. 1 is a schematic illustration of the ultrasonicdevice 10 according to one embodiment of the present invention with aneedle 20 inserted into left ventricular tissue of the heart. The leftventricle is illustrated in cross-section with the mitral valve (thevalve controlling blood flow from the left atrium to the left ventricle)not illustrated. The left ventricle wall 12 is primarily composed ofheart muscle tissue. When the muscle tissue contracts, blood is expelledfrom the ventricle through the aortic valve 14, and into the aorta 16for delivery blood to the body. When the myocardium or muscle tissue isunder perfused, it cannot successfully achieve the function ofdelivering blood to the body.

The ultrasonic device 10 for creating holes includes a handle 18containing an ultrasonic generator or transducer 38 and a needle 20attached at the distal end of the handle. The needle 20 is introducedinto the tissue of the left ventricle starting on the epicardial surface22 and penetrating the myocardial tissue 24. The needle 20 preferablydoes not penetrate the endocardial surface 26. After or during insertionof the needle 20 into the tissue 24 the ultrasonic transducer 38 of thedevice 10 is activated to vibrate the needle longitudinally.

The ultrasonic vibrations of the needle 20 create millions ofmicroscopic bubbles or cavities in fluid, e.g. water, adjacent theneedle. The bubbles expand due to the creation of a negative pressurewhen the needle 20 moves away from the tissue during a vibration. Thebubbles implode violently as the needle moves into the tissue during avibration. This phenomenon, referred to as cavitation, produces apowerful shearing action at the needle tip and causes the cells in thetissue to become disrupted. This disruption causes small blood vesselssuch as capillaries and arterioles to disrupt and form a reversiblehematoma (bruise) type injury to the heart.

The heating of the myocardial tissue 24 by application of ultrasonicenergy creates a zone of reversible tissue damage surrounding the needle20. In accordance with the present invention, the volume of the zone ofreversible tissue damage is preferably maximized while the volume ofpermanent tissue damage is minimized. The reversible tissue damage areaacts like a bruise and causes angiogenesis (creation of capillaries andarteries) and arteriogenesis (creation of small arteries). The newlycreated blood vessels resulting from the ultrasonic treatment improvetissue perfusion and relieve chronic ischemia and angina.

As illustrated in FIG. 1, preferably the needle 20 is inserted into themyocardial tissue 24 so that it does not puncture the endocardialsurface 26. When ultrasonic energy is applied to the needle 20, the zoneof reversible tissue damage created around the needle extends radiallyfrom the needle and axially from the tip of the needle. Accordingly, thezone of reversible tissue damage will preferably extend all the waythrough to the endocardial surface 26. Although FIG. 1 illustratesvisible holes 32 formed though the myocardial tissue 24, in fact, oncethe needle 20 has been withdrawn the holes formed by the needle 20 willbe very small or even imperceptible.

FIG. 2 illustrates one embodiment of the ultrasonic device 10 in whichthe needle 20 is removably attached to the handle 18 and secured in thehandle with a set screw 36 or other securing device. The handle 18preferably includes a metal probe 34 and a transducer 38. The metalprobe 34 transmits ultrasonic energy from the transducer 38 to theneedle 20. The probe 34 may be an aluminum probe having a length ofabout 0.5 to 5 inches, preferably about 1.4 inches. The probe 34preferably has a first larger diameter section for connection to thetransducer 38 and a second smaller diameter section for receiving theneedle 20.

The transducer 38 may be any known ultrasonic transducer which providesultrasonic vibration along a single axis. For example, the transducer 38may include a piezoelectric crystal which vibrates in the ultrasonicrange upon application of an electric voltage. The transducer 38includes a horn 42 which is received within a proximal end of the probe34. The horn 42 is received in a corresponding blind hole 44 in theprobe 34. The transducer 38 causes vibration of the needle 20substantially along an axis of the needle with minimal vibration inother directions.

The transducer 38 is connected by an electrical cable 40 to theregulator 30 which controls the ultrasonic device 10. The needle 20 isoptionally provided with a standard thermocouple 50 welded within thelumen of the needle or on an exterior of the needle. The thermocouple 50is preferably located about 5 mm from the distal tip of the needle 20.The thermocouple 50 is used to give the operator of the device anindication of the temperature of the needle 20 and thus, the temperatureof the adjacent heart tissue. The thermocouple 50 may be any knownthermocouple, such as a thermocouple formed of a chrome alumel andconstantan wire.

According to one preferred embodiment of the invention, lead wires areprovided to connect the thermocouple to the regulator 30 for control ofheating. The regulator 30 may control the temperature of the hearttissue in which the needle 20 has been inserted by controlling theapplication of ultrasonic energy. Since the probe 34 will tend to heatup during operation, preferably a cooling pad 52, illustrated in FIG. 2,is positioned around a distal end of the needle 20 between the probe 34and the tissue. The regulator 30 can be used to ensure that frictionalenergy does not heat the heat tissue to a temperature that willpermanently damage the tissue. It is currently desirable to maintain theheart tissue between 37° C. and 60° C., more preferably between 37° C.and 50° C.

The needle 20 may be made out of a rigid material such as stainlesssteel or titanium. The diameter of the needle 20 can vary, however thepreferred diameters range from about 0.1 mm to about 3 mm with 1 mmbeing presently preferred. The length of the needle can also vary tomatch the left ventricular wall thickness. The needle length ispreferably slightly less than a thickness of the myocardial tissue 24.Preferably, the needle 20 extends about 80-90% of the way through theheart tissue. For example, for tissue about 20 mm thick, a 16-18 mmneedle, and preferably a 17 mm needle will be used.

The very distal end of the needle 20 is beveled to provide a sharp pointfor penetrating the heart tissue. The needle 20 can be fixed to thedistal end of the probe 34, or can be removably attached to the probewith the set screw 36 as shown.

The transducer 38 operates at a frequency in the ultrasonic range, 1 to100 kHz, preferably the transducer operates at 20 kHz or 40 kHz. Thetransducer 38 may operate at 5 to 200 watts, preferably between about 20and 50 watts. The ultrasonic device 10 can measure the temperature atthe thermocouple 50 inside or outside the needle to regulate theapplication of ultrasonic energy by turning the transducer on and off tomaintain a set temperature or temperature range. Presently, atemperature ranging from about 37° C. to about 60° C. is used with atemperature of 37° C. to 50° C. being presently preferred. Theultrasonic energy can be delivered for a set time ranging from 1 secondto 500 seconds, with 30 seconds being presently preferred.

As shown in FIG. 1, at a distal end of the handle 18 is a soft diskshape stop member 48. The stop member 48 may be used to limit thepenetration of the needle 20 into the heart tissue. The stop member 48is preferably formed of a soft flexible material such as rubber whichwill assist the surgeon in holding the needle 20 in place in the hearttissue at the desired depth particularly during beating heart surgery.The stop member 48 may be secured to the needle 20 or to the handle 18such as by epoxy. Alternatively, the stop member 48 may be held in placeby a friction fit.

According to one preferred embodiment of the invention, the ultrasonicdevice 10 is a disposable battery powered device including a batterycompartment within the handle 18 in place of the electric cable 40. Theregulator 30 may also be incorporated within the handle 18 of thedevice.

In use of the embodiment of FIGS. 1 and 2, the needle 20 is insertedinto the heart tissue by a health care practitioner, preferably aphysician, under a procedure that exposes the heart. The needle isplaced such that the needle's distal tip does not penetrate theendocardial surface 26 as shown in FIG. 1. A stop 48 as shown in FIG. 1may be used to limit the penetration depth of the needle 20. Inaddition, to ensure that the needle 20 does not puncture the endocardialsurface 26, appropriate feedback mechanisms can be used such asechocardiography, electrograms, fluoroscopy, and the like. Ultrasonicenergy is then applied to the needle 20 by the transducer 38 causingcavitation of fluid and heating the tissue surrounding the needle tocause reversible tissue damage. The regulator 30 controls thetemperature of the heart tissue to a temperature of about 40° C. toabout 60° C., and preferably about 44 to about 50° C. as sensed by thethermocouple 50. Heating is continued for between about 5 and 120seconds, preferably about 30 seconds. The needle 20 is then removed andthe procedure is repeated as needed to generate an appropriate number ofholes 32 depending on the patients condition. The resulting holes 32 aresurrounded by a relatively large area of reversible tissue damage whichcauses increased angiogenesis and/or arteriogenesis. Over time, theischemic area of the heart which has been treated by the ultrasonicdevice 10 becomes better perfused with blood and the patient with anginaexperiences less pain.

FIGS. 4 and 5 illustrate different needle configurations for differentcavitation effects. The needle 70 in FIG. 4 has a blunt tip 72 with a 90degree angle from the axis of the needle. This blunt tip generatescavitation forces 74 axially distal to the blunt tip. The needle 76 inFIG. 5 has a sharp tip 78 with a 45° angle from the axis of the needle.This generates cavitation forces 80 that spread away from the needle atangles of 45° with respect to the needle axis. Varying the angle of thetip of the needle controls the direction of the cavitation forces.Currently angles varying from about 5° to about 90° are used with anglesof 30, 45 and 60 degrees being presently preferred.

A minimally invasive embodiment of the present invention is illustratedin FIG. 3. The ultrasonic device 60 of FIG. 3 includes a catheter 62which is fed from an access site such as the femoral artery through thevasculature into the aorta 16 and through the aortic valve 14 into theleft ventricle of the heart. An ultrasonic needle 64 is positionedwithin the catheter. The ultrasonic needle 64 is deployed from thecatheter and inserted through the endocardial surface into themyocardial tissue 24. Ultrasonic energy is delivered to the needle 64from an ultrasonic transducer 66 which is positioned outside of the bodyat a proximal end of the catheter 62. The ultrasonic energy istransmitted through the catheter 62 by a flexible shaft 68 to the needle64. Alternatively, the ultrasonic transducer may be provided within thecatheter.

The catheter 62 is preferably constructed out of standard cathetermaterials such as polyurethane, polyimide, and the like. Typically, thecatheter 62 will be extruded via well known means in the art. Thecatheter 62 will have at least one lumen for delivery of the ultrasonicenergy from the transducer 66 to the needle 64. Multiple lumens may alsobe provided for drug delivery, visualization, and the like. The lengthof the catheter 62 is such that it is long enough to place the distalend of the catheter having the needle 64 within the heart from a remoteaccess site such as a femoral artery. A typical catheter for access froma femoral artery is 80 cm to 140 cm long. The diameter of the catheter62 may vary with smaller diameters being preferred. The catheterdiameters may range from about 3 French to about 10 French.

The elongated shaft 68 is used to both deliver the ultrasonic energy tothe needle and to move the needle between an extended and a retractedposition when the catheter has been positioned within the heart.

The minimally invasive ultrasonic device 60 illustrated in FIG. 3operates in substantially the same manner as described above withrespect to FIGS. 1 and 2. The length of the needle 64 is preferablyselected such that the needle does not penetrate all the way through tothe epicardial surface 22 of the heart. This prevents bleeding into thepericardium.

According to an alternative embodiment of the present invention, theapplication of ultrasonic energy can be coupled with another form ofheating such as resistance heating to heat the surrounding heart tissue.Presently, resistive heating of the heart tissue to between 40° C. and60° C. and preferably between 44° C. and 50° C. is used.

According to another embodiment of the present invention, the lumen ofthe needle 20 can be used to deliver beneficial agents to the hearttissue during or after the TMR procedure. For example, a syringe may beattached to a lure fitting of the ultrasonic device for delivery growthfactors into the hole formed by the needle. Examples of growth factorsinclude vascular endothelial growth factor (VEGF), fibroblast growthfactor (FGF), monocyte attracting protein (MAP), and the like.

The method and apparatus according to the present invention provideseveral advantages over the prior art TMR methods employing lasers. Inparticular, the known laser procedure punctures the heart tissue all theway through allowing bleeding into the pericardium and requiring theadditional step of application of pressure to cause clotting orstitching the holes close. The present invention achieves the benefitsof laser TMR without puncturing all the way through the heart tissue. Inaddition, the present invention causes less permanent damage to theheart tissue because it does not remove or vaporize tissue. Becausetissue is not removed, possible overlapping of holes does not create thesame problems in the present invention as in laser TMR procedures.Finally, the TMR procedure according to the present invention employingultrasonic energy is much less expensive than laser TMR.

While the invention has been described in detail with reference to thepreferred embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made and equivalentsemployed, without departing the present invention.

What is claimed is:
 1. A method of performing transmyocardialrevascularization comprising: inserting a needle into heart tissue;applying ultrasonic energy to the needle for a period of time sufficientto create a zone of reversible tissue damage surrounding the needle; andcontrolling the amount of ultrasonic energy applied to the needle basedon a measurement of the temperature of the heart tissue contacting theneedle to heat the tissue contacting the needle to a temperature ofabout 37° C. to about 60° C.
 2. The method of claim 1, wherein theneedle is inserted into the heart tissue from an exterior of the heart.3. The method of claim 1, wherein the needle is inserted into the hearttissue from an interior of the heart by use of a catheter device.
 4. Themethod of claim 1, wherein the needle is inserted into the heart tissuewithout penetrating all the way through a wall of the heart.
 5. Themethod of claim 1, wherein the needle is inserted and ultrasonic energyis applied at a plurality of locations to create a plurality of zones ofreversible tissue damage.
 6. The method of claim 1, wherein theapplication of ultrasonic energy to the needle heats tissue surroundingthe needle to a temperature of about 40° C. to about 60° C.
 7. Themethod of claim 1, wherein the ultrasonic energy is applied at afrequency of about 1 to 100 kHz.
 8. A method of treating ischemia andangina by causing reversible damage to myocardial tissue, the methodcomprising: inserting a needle into the myocardial tissue; applyingultrasonic energy to the needle; and controlling the amount ofultrasonic energy applied to the needle to heat the myocardial tissuecontacting the needle to between about 40° C. and about 60° C. to createa zone of reversible tissue damage around the needle.
 9. The method ofclaim 8, wherein the ultrasonic energy is applied at a frequency ofabout 20 to 40 kHz.
 10. The method of claim 8, wherein the needle isinserted into the endocardial and myocardial tissue and does notpuncture the epicardial tissue.
 11. A method of treating isehemia andangina by causing reversible damage to myocardial tissue, the methodcomprising: inserting a needle into the myocardial tissue wherein theneedle is inserted into the epicardial and myocardial tissue and doesnot puncture the endocardial tissue; applying ultrasonic energy to theneedle; and heating the myocardial tissue to between about 40° C. andabout 60° C. to create a zone of reversible tissue damage around theneedle.
 12. A method of performing transmyocardial revascularizationcomprising: inserting a needle into heart tissue, the needle including asolid distal tip; applying ultrasonic energy to the needle for a periodof time sufficient to create a zone of reversible tissue damagesurrounding the needle; and controlling the amount of ultrasonic energyapplied to the needle based on a measurement of the temperature of theheart tissue contacting the needle to heat the tissue contacting theneedle to a temperature of about 37° C. to about 60° C.
 13. A method fortreatment of tissue comprising: inserting a needle into the tissue;applying ultrasonic energy to the needle for a period of time sufficientto create a zone of reversible tissue damage surrounding the needle; andcontrolling the amount of ultrasonic energy applied to the needle basedon a measurement of the temperature of the tissue contacting the needleto heat the tissue contacting the needle to a temperature of about 37°C. to about 60° C.
 14. The method of claim 13, wherein the tissue isheart tissue.
 15. The method of claim 14, wherein the needle is insertedinto the heart tissue from an exterior of the heart.
 16. The method ofclaim 14, wherein the needle is inserted into the heart tissue from aninterior of the heart by use of a catheter device.
 17. The method ofclaim 14, wherein the needle is inserted into the heart tissue withoutpenetrating all the way through a wall of the heart.
 18. The method ofclaim 13, wherein the needle is inserted and ultrasonic energy isapplied at a plurality of locations to create a plurality of zones ofreversible tissue damage.
 19. The method of claim 13, wherein theapplication of ultrasonic energy to the needle heats tissue surroundingthe needle to a temperature of about 40° C. to about 60° C.
 20. Themethod of claim 13, wherein the ultrasonic energy is applied at afrequency of about 1 to 100 kHz.